1. Field of the Invention
This invention generally relates to rack mounted modular components such as shelf or box mounted electronics and computer components and more particularly to a latching apparatus for positive insertion and latching of modular housings in a rack mounted enclosure.
2. Description of the Related Art
Conventional computer hard disk drives adapted for use in mainframe and large server applications such as commercial installations are currently packaged in electronic component modules, such as hard disk drive modules, which are installed side by side in a five sided enclosure or shelf unit which is in turn mounted in a vertical rack of similar shelves. These hard disk drive modules are typically conventional 31/2 inch form factor high performance drives each enclosed by a module housing about 33/4 inch by 2 inches by 61/2 inches. In order to positively secure these modules in the shelf which has the required number of electrical peripheral connectors on its internal back plane, these module housings typically have some kind of latch on the front which engages a corresponding recess in the shelf to ensure the module is fully inserted and to keep the module from popping out of its back plane socket.
A major disadvantage with conventional latch designs being used is that a large amount of finger force is required to either latch or unlatch the module from the shelf. In addition, the module latches are difficult to grasp. Therefore the individual who frequently need to remove and install these modules often simply starts to insert the module in the slot or space available and then slams the module into the shelf, sometimes repeatedly, in order to make solid connection with the latch and the connector on the back plane without having to separately exert force on the module housing to latch the module housing in place.
A direct consequence of this slamming into the back plane connector is that unacceptable and damaging capacitive in rush or startup currents may be generated during the power-up of the module. Typically, these modules may be "hot-plugged" into the back plane. In other words, a cold, i.e. unenergized, module is connected into a connector already having its 5 volt power pins energized. The pins on these connectors are designed so that power and ground are applied before the output and signal connections are made. This is accomplished by making these pins longer so that they are engaged with their mating sockets before the output and signal connection pins and sockets are mated. This difference in length prevents in rush or surge currents from damaging module subcomponents when a module is inserted by hand with normal force and speed. Also, a resistance is provided in series with these power pins to minimize the effect of in rush current which does occur when they are hot plugged. These two features cooperate to prevent undesirable currents from being generated during power-up under normal operating conditions.
However, when the individual slams a module into a bay slot and into connection with the connector on the back plane, there is only about a millisecond or less between mating of the power pins and sockets and the mating of the output and signal pins and sockets. Consequently there is insufficient time for the power supply voltage to be fully developed, i.e. rise to a constant level, within the module before signal pin mating, and abnormal in rush currents are generated which can damage internal components, generate false signals to other peripheral devices or to the computer, and/or destroy stored digital information.
Another problem with conventional module latching mechanisms is that they are usually located on the front end face of the module housing. Accordingly, these latching mechanisms cannot be used on modules with removable media, or modules which contain other peripheral devices such as tape drives, CD-ROM drives, PCMCIA card carriers, etc., all of which require access through the end face in order to insert or remove the removable internal components.
Therefore there is a need for an apparatus which prevents the buildup and transfer of harmful startup currents during hot installation and/or removal of modular components. There is also a need for an apparatus which assists the operator with insertion so that there is no need or desire to slam the module into the shelf. There is also a need for a latching apparatus which can positively lock the module in place to prevent unauthorized removal and inadvertent removal of the module.